This invention relates to enhancing combustion in an internal combustion engine by means of a combustion enhancing insert in the cylinder that reduces the amount of unburned fuel that typically collects in the cylinder and allows for an increase in the compression ratio without increasing the piston height.
In internal combustion engines, a cylinder houses a reciprocating piston as shown in FIG. 1. As the piston moves up, fuel is sprayed into the combustion area that is compressed as the piston moves and combustion takes place. Combustion product gases are naturally directed toward the cylinder liner by the high velocity injected fuel. The gases at the front of the spray plume from the fuel injector are often only partially burned and contain the highest levels of soot, CO, and unburned hydrocarbons. High turbulence levels and high temperatures are usually necessary for the complete oxidation of these partially burned species. The high velocity injected fuel forces these gases toward the cylinder liner that is much cooler than the reacting gases in the combustion area in the piston bowl. This area near the liner where the gases collect, between the piston land and the cylinder head at the top of piston travel or "top dead center," is called the the "squish area."
Gases that collect in the squish area are a toll on fuel efficiency and emissions because more fuel needs to be burned to make up for the gas that collects in the squish area. Consequently, preventing gases from entering the squish area is beneficial to both low emissions and high fuel efficiency.
In addition, there is normally a gap between the piston and the liner called the "crevice area." The squish area and the crevice area combined is referred to herein as the "end gas area." The crevice area represents an unproductive area that increases heat loss and has a net effect of increase in production of emissions of Nox, smoke, soot, CO, and unburned hydrocarbons. The crevice area thus tends to be an area where soot particles collect in diesels and spark ignition engines. Soot particles in the crevice area may migrate to the engine lubricating oil and shorten the life of the oil while also shortening the life of the engine. Soot particles may also enhance deposit formation in the crevice area and on the top compression ring of the piston that leads to failure of the top compression ring and ultimately to loss of compression and oil control.
Compression ratio is defined as the volume between the piston and cylinder head at the bottom of piston travel over the volume between the piston and cylinder head at top dead center. Generally speaking, a high compression ratio is desirable in engines because a high compression ratio increases fuel efficiency. However, engines that have a low stroke/bore ratio do not have sufficient clearance between the piston and valves at top dead center to accomplish high compression ratios (16:1 or higher). As a result, it would be beneficial to accomplish high compression ratio without increasing the piston height.
One method of reducing the crevice area is to move the top compression ring higher toward the top of the piston land. However, this method leads to excessive ring temperatures and accelerated depositing on the top compression ring, which leads to failure of the top compression ring. Another method uses a scraper ring, a ring embedded in the cylinder liner that scrapes off deposits in the crevice area as the piston moves up and down. However, the scraper ring does not prevent gases from collecting in the squish area and does not allow for an increase in the compression ratio.
Therefore, it is apparent from above that there exists a need in the art for improvements in combustion within an internal combustion engine.